Communication systems are widely used in computer and device networks to communicate information between computers and other electronic devices. Transceivers of a communication system send and receive data over a link (including one or more channels) of a communication network to communicate with other transceivers. A transceiver includes a transmitter for sending information across a link, and a receiver for receiving information from the link. The receiver detects transmitted data from a link partner transceiver on the opposite end of the link and converts the data into a form usable by the system connected to the transceiver. For example, one widely-used network communication standard is Ethernet, including several different standards for different network bandwidths, including 10 GBASE-T allowing 10 gigabit/second connections over unshielded or shielded twisted pair cables.
There are multiple sources of impairment and interference in a 10 GBASE-T system which can cause significant performance degradation. These sources of impairment and interference can be broadly categorized as internal and external sources. The internal sources are caused by the link partners themselves and imperfect channel characteristics. Some examples of these sources are inter-symbol interference (ISI), echo and pair-to-pair cross-talk such as far-end crosstalk (FEXT) and near-end crosstalk (NEXT). Other examples of internal interference include differential skew between the two differential signal components in the channel (e.g., imbalance in the channels) and driver circuit asymmetry generating different transition for rising and falling edges (e.g., imbalance of the differential drivers). Typical causes of imbalance in the channels include, for example, unequal stray coupling of the traces (or wireline), differences between two trace widths, propagation time differences caused by woven printed circuit board (PCB) substrate, change in PCB layer and coating on micro-strips, transformer unequal windings for the two differential signal components, and crimping of the wires in the plug and in connection to connectors. Typical causes of imbalance of the differential drivers include, for example, termination impedance mismatch, and differential switching circuitry not having the same response for the respective falling and rising edges.
In some cases, differential signal imbalance may lead to levels of common-mode that cause undesirable RF emissions during signal transmissions along the channel. Transceiver designs often must meet stringent Federal Communications Commission (FCC) rules and regulations regarding spurious emissions in order to avoid interfering with other communications equipment. Thus, common-mode problems should be periodically addressed to properly stay within FCC guidelines.
Accordingly, in order to reach the desired performance of high bandwidth communication systems, it would be desirable to have systems and methods that compensate for differential signal imbalances in communication system transceiver circuitry, providing more robust communication in such systems, and maintaining FCC compliance.